From what I can make out the plan is to move everyone onto a single code base (4.0). Those who have Odyssey will have access to everything, while those still on Horizons will have certain things 'disabled' at certain 'choke points', such as not having a 'disembark' option from either their ship or SRV and not being able to land or plot a taxi to an atmospheric planet settlement (Edit: as they can never disembark, they'll never be able to book a taxi, so that's a moot point). Otherwise both 'versions' will essentially be the same, down to previously Odyssey only content such as the Scorpion, which will be offered to Horizon players either as a sign of good faith or because they can't easily disable access to those new features.
Three issues delayed this move; the host of bugs, particularly performance related ones, that were present at launch, which have been 'sufficiently' resolved. Console compatibility, which has been resolved by abandoning console development. And finally the remaining problems with planetary tech which were resolved by abandoning any further attempts to resolve them. Yes, I'm aware of the irony of the latter two issue resolutions.
This will leave one single PC code base and a console version(s?) that will be put on life support. Commercially all of his this makes perfect sense and probably was planned for Q3 of 2021, were it not for the botched launch.
As for the Azimuth resolution, and the game narrative moving forward, that's anyone's guess, but I suspect they're going to try something radical, on the same level as the World of Warcraft Cataclysm update, to reinvigorate the franchise.